<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var num = 1;
        var str = 'abc';
        var bool = true;
        var mynull = null;
        var myundefined = undefined;
        console.log(num)
        console.log(str)
        console.log(bool)
        console.log(mynull)
        console.log(myundefined)
        // 一眼就看出来的就是字面量
    </script>
</body>
</html>